Apparatus for the high speed, low pressure gas jet deposition of conducting and dielectric thin sold films

ABSTRACT

Described is a method for depositing from the vapor phase a chemical species into the form of a thin solid film material which overlays a substrate material. The deposition process consists of three steps: (1) synthesis of depositing species, (2) transport of said species from site of synthesis to a prepared substrate material, and (3) condensation and subsequent film growth. The transport step is achieved by admixing small concentrations of the depositing species into the flow of a high speed jet of an inert carrier gas. This jet impinges on the substrate&#39;s surface and thereby convects the depositing species to this surface where condensation occurs. Since the gas mixture is at fairly high pressure, the deposition is achieved in a simple flow apparatus rather than in the high vacuum systems required of other methods. Also this transport technique allows the chemical and/or physical phenomena utilized in the depositing species synthesis step to be isolated from the actual condensation reaction. Consequently, the conditions governing each of these reactions can be varied independently to optimize both steps. Such flexibility permits the synthesis and deposition of a wide variety of chemical species, hence many thin film materials are susceptible to formation by this method.

This is a continuation of application Ser. No. 08/132,122 filed on Oct.5, 1992, now abandoned, which is a continuation of application Ser. No.08/001,895 filed on Jan. 7, 1993, now abandoned, which is a continuationof U.S. Ser. No. 07/277,234, filed Nov. 29, 1988 now abandoned; which isa divisional of U.S. Ser. No. 06/888,590, filed Dec. 12, 1985 as thenational phase of PCT/US85/00219, filed Feb. 12, 1985, and issued onNov. 29, 1988 as U.S. Pat. No. 4,788,082; which is acontinuation-in-part of U.S. Ser. No. 06/579,676, filed Feb. 13, 1984,(abandoned).

This application is a divisional application of Ser. No. 888,590 filedon Dec. 12, 1985, Ser. No. 888,590 being a continuation-in-part of Ser.No. 579,590, filed on Feb. 13, 1984.

FIELD OF THE INVENTION

This invention relates generally to the field of thin solid film coatingdeposition technologies which are techniques for fabricating materialsin the form of a thin solid film coating on a substrate material. Inparticular, the invention described herein makes possible deposition ofboth old and new materials under conditions of lower vacuum thanrequired by other technologies. Such coating materials can have unusualand remarkably useful properties, especially in the areas ofelectronics, optics, wear surfaces, protective coatings, catalyticmaterials, powder metallurgy, and biomedical implant surface coating.

BACKGROUND OF THE INVENTION

In recent years, in the prior art much effort has been directed towarddevelopment of economically viable techniques for manufacturing varioususeful materials in the form of thin solid films which overlay asupporting solid substrate material, such as corrosion resistantmaterials, which provide chemical protection for the supporting material(e.g. an oxide coating on an aircraft engine's turbine blades). Thereare many differing technologies in use today, yet they can all beclassified under one of the following five catagories:

1) Physical Vapor Deposition

2) Chemical Vapor Deposition

3) Electro--and Electroless Deposition

4) Thermal Spraying methods

5) Polymeric Coating methods

However, all these diverse methods involve the following three steps:(1) Synthesis of the depositing species; (2) Transport of the depositingspecies from its source or place of synthesis to the site of deposition;(3) Deposition and subsequent film growth.

It is recognized in the prior art that the same thin film material maybe susceptible to formation by several different techniques. Forexample, thin films of amorphous hydrogenated silicon, which can be usedin solar power conversion technology, may be fabricated by threeradically different techniques: (1) Plasma deposition; (2) Sputteringand (3) Chemical Vapor Deposition (see e.g. M. H. Brodsky, "PlasmaPreparation of Amorphous Silicon Films", Thin Solid Films 50, 1978Elsevier Sequoia S. A., Lausanne--The Netherlands; T. D. Moustakas, etal, "Preparation of Highly Photoconductive Amorphous Silicon by RFSputtering", Solid State Communications 23, 1977 Pergamon Press--GreatBritain; S. C. Gau, et al, "Preparation of Amorphous Silicon Films byChemical Vapor Deposition From Higher Silanes", Applied Physics Letters39 (5), 1981 American Institute of Physics). Often an innovation indeposition technology manifests itself not as a direct improvement inthe product material, but rather as an economic improvement in theprocess technique. The use of simple flow systems in the apparatus andmethod of my inventions improve the process of deposition of thin filmmaterials over that of the prior art which required complicated highvacuum apparatus. The result also makes possible synthesis anddeposition of new structures of known chemical species.

SUMMARY OF THE INVENTION

My inventions allow one to produce a useful thin solid film material bydepositing from the gas-phase a saturated chemical vapor species onto asubstrate material through the use of a high speed jet of inert carriergas to transport the depositing chemical species--present in diluteconcentrations in the carrier gas--from the site where the synthesis ofthe depositing vapor species occurs to the substrate material wherecondensation and deposition occurs.

Other objects, advantages, and novel features of my inventions, as wellas the need and motivation for using the broad term "useful thin solidmaterial", will without departing from my inventions become apparent tothose skilled in the art both now and in the future upon examination ofthe following detailed description of the preferred embodiments of myinventions. In a preferred embodiment of an apparatus useful for myinvention, there is a nozzle, and a chamber downstream of the nozzletermed herein the deposition chamber. An inert flowing gas acts as thecarrier fluid. A mechanical pump induces a steady flow of the inertcarrier gas from the gas supply through an inlet. The flow proceedsthrough the nozzle into the deposition chamber, where it forms a jet.The flow exits via an outlet. If desired, the carrier gas may berecirculated by a recirculation loop. Within the deposition chamber ispositioned the substrate on which the product thin film is deposited.The nozzle and the substrate may move relative to one another in orderto change the area of the substrate's surface which is directly underthe nozzle and thereby coat a larger portion of that surface. Atransport mechanism achieves this motion by moving the substrate.(Alternately, the nozzle could be mounted on a mechanism which moves itrelative to a stationary substrate). An apparatus for heating and/orcooling the substrate is also useable, as well as a means for heating orcooling the carrier gas before it enters the nozzle through the inlet. Aport provides access to the deposition chamber. The regions R1 and R2 ofthe flowfield, are significant in the description of the depositionprocess which follows below.

Also provided is a specific example of the preferred method in which aparticular material is deposited, in this case: tungstic-oxide. Inaddition to the general features of the apparatus described above, thereare also features necessary for the deposition of tungstic-oxide. Thecarrier gas is helium (although any other inert fluid could also beemployed). A dilute concentration of oxygen which has been premixed inthe helium contained in the gas supply enters through the inlet. Thereis a tungsten filament (which is a solid cylindrical rod orientedtransverse to the plane of helium flow), evaporated tungsten atoms andtungstic-oxide radicals. The tungstic-oxide deposit is formed on theprepared substrate. The method for the formation of a tungstic-oxidedeposit is described below.

As an important portion of the above apparatus description, there is thenozzle exit region of the flowfield, which contains the part of the flowregion R1 furthest upstream in the flow. The nozzle walls represent theend of the converging part of the nozzle, the nozzle throat, and exit.There is a flow of the inert carrier gas through the nozzle. A saturatedchemical-vapor species originates at some source centered in theflowfield. The flow of the carrier fluid entrains this condensiblemolecular species and convects them through the nozzle and beyond thenozzle exit. The region of the flowfield which contains condensiblespecies is termed herein region R1.

Further described is one mechanism for introducing chemical reactionprecursor species as dilute components in mixture with the flow of theinert carrier fluid. The nozzle and inlet as well as the inert carriergas are used here, along with the remainder of the apparatus describedabove. For this mechanism, an undersaturated vaporous precursor specieshas been premixed in the carrier fluid upstream of the inlet.

Further described is an additional mechanism for introducing precursorspecies into the flow of the carrier fluid. Again, the nozzle, inlet,and inert flowing gas are used, and the remaining features of theapparatus described above. In this mechanism, the precursor species ispresent initially in solid or liquid state. This solid or liquidmaterial is held in place in the flowfield, and is then heated toevaporate (or sublime) molecules off into the gas-phase. These moleculesare entrained in the flow of the carrier gas and convected through thenozzle.

Further described is another method of precursor species introduction.Again, the nozzle, inlet, and inert flowing gas are used. The remainderof the apparatus described above is assumed also to be used. In thismechanism, the reactant species are in gas or liquid phase, and areintroduced via a thin tube which exits into the region R1. The reactionprecursor species is assumed to originate from a supply source.

Further described is a nozzle with a diverging section (often termed aLaval nozzle). The flow of the gas is accelerated through the convergingsection of the nozzle until it reaches the nozzle throat, which is thepoint of greatest constriction. Beyond the throat, the flow is stillcontained within the diverging section (in contrast to a nozzle withexit at the end of the throat). The flow of gas exits at the end of thediverging section and forms a jet. Such a nozzle would be substituted inthe apparatus described above for the nozzle previously described havingonly a converging section.

Further described are the flow of the carrier gas past--and thedeposition of the condensing species on--three types of substratesdifferentiated by their geometries. These substrates would besubstituted for the substrate previously described. The carrier gas jetand the remainder of the apparatus previously described are assumed tobe in place. Described are three possible generalized cases of substrategeometry and the consequent effect of these cases on the flow field ofthe gas mixture and the deposition process.

Further described is one case of the flow of the jet past a generalized"bluff body" or substrate of low or zero curvature. Curvature must becompared to the width of the jet. The streamlines of the carrier gas jetimpinge on the surface and then flow along the surface away from thesite of impingement termed herein the "stagnation point". The moleculesof the depositing species are convected by the carrier gas flow to thesubstrate surface where they condense to form the thin film coating. Thedeposition is most concentrated at the stagnation point.

Further described is a second case of the flow field around a"sharp-edged" substrate, with its edge directed into the flow of thejet. In this case, the stagnation point occurs at the edge itself andthe deposition is concentrated there. Again, the molecules of thedepositing species condense to form a thin film coating.

Further described is a third case of the jet's flow past a substrate oflarge curvature. Curvature must be compared to the width of the jet. Inthis case, the streamlines of the carrier gas jet flow around thesubstrate and rejoin downstream. The molecules of the depositing speciesare convected by the carrier fluid to the substrate's surface where theydeposit to form a thin film coating. In this case too, there is astagnation point at which the deposition will be most concentrated.Further described is the concept of employing the mechanism of theapparatus previously described to move the substrate relative to the jet(or the nozzle, since the jet is emitted from the nozzle). Alternately,there may be a mechanism that moves the nozzle relative to a stationarysubstrate. Therefore to illustrate the general notion of substratemotion relative to the jet, only the jet and the substrate are discussedhere, although the remainder of the apparatus previously described isassumed to be in place here as well. Also, for the purposes ofillustration, a "bluff body" substrate is described here, although a"sharp-edged" substrate or a substrate with large curvature relative tothe jet's width could be substituted for the substrate as well. Thepoint to be illustrated is that as the substrate is moved relative tothe jet, the stagnation point of the carrier gas flow--which is also thesite where the deposition of the condensing species is most concentrated-moves across the surface of the substrate. Thus, there is not just onepoint on the substrate's surface where deposition is concentrated, butrather the concentrated deposition occurs across the surface, and if themotion is at a uniform rate (also, of course, assuming the condensingspecies arrive at the stagnation point at a constant rate) then a thinfilm of uniform thickness will condense on the substrate's surface.Further described is the use of the apparatus previously described in"batch mode" for the coating of "batches" of substrates. The jet and therest of the apparatus previously described is assumed to be in place.Substituted for the substrate previously described is a mechanism forholding and transporting individual substrates into and through the flowof the jet where they receive their thin film coating as the jettransports the condensible species to the surface of the individualsubstrates. The "sharp-edged" substrates may be individual substrates orthe other substrate geometries are also possible individual substratesfor the "batch mode". All the individual substrates are contained in thedeposition chamber previously described. After the entire batch ofsubstrates are coated, the deposition is complete, and the depositionchamber is opened to remove the coated substrates.

Further described is the use of the previously described apparatus in"semi-continuous" mode of deposition. The jet and the balance of theapparatus previously described are also assumed to be in place. Thesubstitute here is in the form of rolled stock (e.g. rolled sheetmetal). This rolled stock is unwound from one spool, passed through thejet which transports the condensible species to its surface, andreceives its thin film coating at the stagnation point. Finally, thecoated substrate stock is rewound on another spool. Both spools arecontained within the deposition chamber. After the rolled stock iscoated and rerolled on the receiving spool, the deposition is complete,so the deposition chamber is opened and the coated substrate removed.Both "bluff body" substrates--e.g. rolled sheet metal--or substrateswith large curvature--e.g. coiled wire--may be coated with thin filmmaterial in the "semi-continuous" mode. Even "sharp-edged" substratesmay be coated in this manner provided they are capable of being rolledor coiled.

Further described is the use of the apparatus previously described forthe production of powdered materials as used in metallurgy. The jet andthe entire apparatus previously described is assumed to be in place.Substituted for the substrate previously described is a rotating drum(with sides which act as a target surface area where condensationoccurs). The jet transports the depositing species to the surface of thedrum where deposition occurs at the stagnation point. As the depositingspecies condenses and forms a thin film coating on the rotating drum,the thin film material subsequently revolves around with the drum, andencounters a scraper which removes the material from the drum. Thismaterial, in powdered form, is collected in a hopper. The entireapparatus is contained within the deposition chamber previouslydescribed. When the hopper is filled with the powder, the depositionprocess is discontinued, and the deposition chamber is opened to removethe powder for use in powder metallurgy. Also described are heating andcooling mechanisms for heating and/or cooling the drum surface tofacilitate the deposition and powdering processes.

Further described is an alternate embodiment of the apparatus previouslydescribed, wherein an apparatus is substituted for the substrate, and isused for the production of thin sheets of material. The jet and theremainder of the apparatus previously described is assumed to be inplace. The jet transports the depositing species to the surface of arotating drum, (which acts as a target condensation area) where thatspecies condenses at the stagnation point to form a thin film. The drumrotates and the film encounters the scraper which peels the film off thedrum so that the material is in the form of a thin sheet. A mechanismpulls and transports the sheet material off the drum. The entireapparatus is contained within the deposition chamber previouslydescribed. After fabrication of the sheet material, the depositionprocess is complete and the chamber is opened so that the sheet stockcan be removed. Mechanisms for heating and/or cooling the drum tofacilitate the deposition and peeling processes are described.

Further described with respect to FIG. 1 is the experimental apparatus10. The gas flow originates in a storage cylinder 12, and enters theapparatus via a pipe 14 through an inlet 16. The flow is regulated witha needle valve, and a throttle valve not shown. The pressure upstream ofa small orifice 18 in a nozzle 20 is measured by a mercury manometerattached to the flow system. The flow pressure upstream of the nozzle ismeasured by an oil manometer not shown. The gas flows through the nozzleinto a deposition chamber 22, which is a glass bell jar. The lowerpressure in the deposition chamber is measured with an oil manometer.The gas flow forms a jet 24 as it exits the nozzle, which jet impingeson a substrate 26 (usually a microscope slide). The nozzle to substratedistance may be adjusted with a thumbscrew not shown. A tungstenfilament 28 is placed just upstream (within one nozzle diameter) of thenozzle throat section. A line-of-sight is maintained to the filament, sothat a measurement of its temperature can be taken using an opticalpyrometer. The flow finally exits through a throttle valve 30 and ispumped away by a rotary pump 32.

Further described are the cross-sections of two nozzles used in theexperimental demonstrations. Both were of conical symmetry and were madeof brass.

Further described are the cross-sections, and throat dimensions of twonozzles used in experiments. These are made of brass.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified schematic illustration of an apparatus providedin accordance with the present invention.

FIG. 2 is a detailed schematic illustration of a portion of theapparatus of FIG. 1.

FIG. 3 is a detailed schematic illustration of a portion of the nozzleof the apparatus of FIG. 1.

FIG. 4 is a simplified schematic illustration of a portion of a nozzleused with the present apparatus illustrating a solid precursor species.

FIG. 5 is a detailed schematic illustration of a portion of the nozzleof the apparatus of FIG. 1, including a tube for providing precursorspecies.

FIG. 6 is a simplified schematic illustration of a portion of asubstrate receiving material in the present apparatus.

FIG. 7 is a simplified illustration of a substrate used in the presentapparatus having a series of raised ridges.

FIG. 8 is a simplified schematic illustration of a wedge-shapedsubstrate used with the present apparatus.

FIG. 9 is a simplified schematic illustration of a rounded substrateused in the present apparatus.

FIG. 10 is a simplified illustration showing a cylindrical or wire feedsubstrate used with the present apparatus.

FIG. 11 is a simplified illustration showing a rotating substrate usedwith the present apparatus.

FIG. 12 is an alternative embodiment of a rotating substrate similar tothat shown with respect to FIG. 11.

FIG. 13 is a simplified illustration showing a mechanism for laterallymoving the substrate an apparatus provided according to the presentinvention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Since my invention departs so greatly from prior practices, I willdescribe some of the theory behind my invention. The modern theory ofPhysical Chemistry tells one that a chemical reaction is completelyspecified by the thermodynamic variables such as pressure, temperature,etc. which govern the molecular behavior of that reactions constituentchemical species, along with the specific reaction mechanisms andassociated activation energies (which energies may be introduced byradiation, thermal conduction, etc.). Because this deposition techniqueaffords great flexibility and control in specifying these variables,there are a large number of chemical reactions which potentially couldbe induced to occur by the following described method. The final productof such reactions is the desired useful phase of a solid in thin filmform. This may be deposition on a substrate, where it remains, but alsoalternately collected at a target area from which it can be removed asdescribed above. This alternate embodiment may be preferred in, say,powdered metallurgy uses.

Rather than trying to present an exhaustive list of all possible andanticipated useful reactions, the following summary will treat thegeneral problem of depositing a thin film by the present technique, asembodied in my preferred embodiments in the three steps:

1) Synthesis or formation of depositing vapor species

2) Transport of said species from source to substrate

3) Condensation of species and film growth.

Using the three steps of my process, the general problem of condensing achemical species from the vapor phase into the form of a useful thinsolid film, which coats the surface of a supporting solid material, maybe solved with new results.

By the use of the high speed mass flux of an expanding inert gas as acarrier mechanism for transporting a dilute concentration of a saturatedmetal-vapor species from the site where that species was synthesized tothe object to be coated, where the condensation occurs, a thin solidfilm product may be formed (metallic or metal-compound). The advantagesin using this system are manifold. Foremost is that the inert carriergas transports the saturated metal-vapor so quickly that there is notime for condensation to occur on anything except the object to becoated (i.e. unintentional depositions on the apparatus' chambers' wallsare largely avoided). Thus nearly 100% of the synthesized depositingspecies is used in forming the thin film. Other advantages include theutilization of the full flexibility of gas-phase chemistry for formationof the depositing species; the system allows high depositing rates; themechanism is continuously self purging; and it affords independentcontrol of the quench rate. The last advantage arises because thesubstrate temperature during condensation can be varied at will.

A preferred embodiment of an apparatus useful for my inventions isdescribed as noted above. There is the nozzle and a chamber downstreamof the nozzle termed herein the deposition chamber. An inert flowing gasacts as a carrier fluid. The mechanical pump induces a steady flow ofthe carrier gas from the supply through the inlet and nozzle. The fastmoving gas flowing through the nozzle enters the deposition chamber andforms a jet. It is this jet which impinges on the substrate thatachieves the transport of the depositing species. The depositing speciesmay be synthesized in a region 34 of the flow field, which extends fromjust upstream of the nozzle or orifice, through the throat region, andextends the length of the jet. The deposition occurs in region 38 whichborders the surface of the substrate. Finally, the gas exits via theoutlet and is exhausted or if desired the carrier gas may berecirculated via a recirculation loop 40. The substrate is prepositionedin the deposition chamber, on which the product thin film is deposited.A transport mechanism 76, FIG. 13 moves the substrate past the nozzleand through the jet. An alternate embodiment, which may be preferred,would include a mechanism causing the nozzle, and therefore the jet tomove relative to a stationary substrate. The jet is caused to be movedrelative to the substrate in order to coat a larger area of its surface.A mechanism heats and/or cools the substrate during the deposition inorder to facilitate the fabrication of the thin film. Also a mechanismheats or cools the carrier gas in order to facilitate the transport ofthe depositing species, and to optimize the thermodynamic conditionsgoverning the synthesis and condensation reactions. A port allows accessto the deposition chamber before and after the deposition process.

The flow geometry, flow speed and the carrier gas pressure can bearranged so that the synthesis of the depositing saturated vapor speciesoccurs near the center of the forming jet and does not allow time fordiffusion of those species to the walls of the apparatus which borderregion 34 as shown in an enlarged view in FIG. 2. The saturated speciesoriginates at some source centered in the flow field of the inertcarrier fluid. The fast moving carrier fluid convects the saturatedspecies past the nozzle's throat's walls, before that species has timeto diffuse to them. In this manner, unwanted condensation on thethroat's walls is avoided. The depositing species is transported beyondthe nozzle exit into the deposition chamber, and the flow nowconstitutes a free jet.

The flow speed of the jet slows as it encounters the solid substrate inflow region 38, and here the saturated vapor species migrates to theobjects solid surface where they form a deposit. The inert carrier andany unreacted gaseous reaction precursor molecules flow downstream andare pumped out at an exit. If a gas mixture containing unreacted gaseousspecies is recirculated via a recirculation loop then these reactants aswell as the carrier gas are recovered for further use. Furtheramplifications of the general deposition process follow below.

A specific example of the method is described now so as to give aconcrete example that will illuminate the generalized discussion of thedeposition method which follows below. All the features of the generalapparatus previously described are used. Also included are theadditional specific elements necessary for deposition of a particularmaterial: tungstic-oxide. A gas mixture, which originates in the supplyand contains dilute concentrations of oxygen in helium enters throughthe inlet and flows over the tungsten filament (a solid tungstencylinder). An electric current from a power supply is passed through thetungsten filament to resistively heat it to temperatures at whichevaporation of tungstic-oxide occurs. The oxygen in the flow reacts withthe hot solid filament to form a surface oxide. This oxide evaporatesdue to the high temperature of the tungsten filament, and thetungsic-oxide vapor molecules are entrained in the helium flowing aroundthe filament. These saturated vapor molecules (saturated because thehelium stream is cool) are convected by the flow downstream to the coolsubstrate where they condense to form a tungstic-oxide deposit.

According to the invention, the thin solid film is produced in a processof which my various preferred steps are described below:

1. Synthesis of Depositing Species.

This step may be achieved in several ways exploiting physical and/orchemical phenomena as described below. It will be important to observethat in my process, all vapor species which will saturate at theprevailing gas temperature must be confined to region 34 of the flowfield. This temperature may be varied over a wide range to avoidpremature condensation of a given reactant species by employing the gasheating/cooling mechanism of the apparatus previously described--but itis anticipated that for many reactions the gas need only be at roomtemperature. All experimental demonstrations were performed withunheated gases, but the only theoretical limit on the gas temperature isthat it must be cool enough in flow region R2 for condensation to occurin the desired manner. The important point is that once a saturatedvapor species is formed in region 34, it must be transported so quicklythat it does not have time to condense on the nozzle's walls. Thus, theproblem becomes one of delivering the reaction precursor molecules tothe region R1 and inducing a reaction to occur which synthesizes thedepositing species.

This delivery can be achieved in three distinct ways: 1) The precursor(or precursors) may be a vapor or gas species 42, FIG. 3, which is inundersaturated in the gas-phase at the prevailing temperature of thecarrier gas. Then it can be mixed into the carrier far upstream andintroduced into region 34 along with the carrier's flow through thenozzle, where the precursor is then acted upon to synthesize acondensible species. (A description of such actions follows shortly.)This mechanism may be employed to introduce metal-bearing gaseousmolecules (say silane or an organo-metallic salt) which is then used tosynthesize a depositing metal-vapor, or it may be used to introducereactive gas (say oxygen or a halogen) which reacts with a metal vaporin the formation of a metal-compound deposit (say a metal-oxide). Or 2)the precursor species may be in solid or liquid form (44, FIG. 4) as amaterial, which is held in place directly in the flow field of gasthrough the nozzle at region 34 and subsequently heated e.g. byresistive heating of the material itself, or through contact with aheated surface, or with a laser) to evaporate (or sublime) offmolecules, which then become entrained in the carrier gas flow. Or 3)the reactant species may be molecules of a fluid 46, FIG. 5 injected viaa thin tube 48 into the flow region 34, where they are entrained in theflow of the carrier gas through the nozzle.

Each mechanism can be used multiply in the same apparatus, in order tointroduce several species, i.e. there can be two or more reactants,premixed in the carrier fluid (mechanism 1); or several solid or liquidmaterials placed in the flow (mechanism 2); or several thin tubesexiting in the region 34, each transporting a different species(mechanism 3). All three methods may be used simultaneously to delivertwo or more reactant species to region 34 to achieve synthesis of thedepositing species. As a specific preferred embodiment, tungstic-oxidethin films may be formed in a process utilizing delivery mechanisms 1and 2.

The introduction by evaporation from a solid (mechanism 1) produces asolidifiable vapor species, and so no other actions are necessary toachieve deposition. The evaporated atoms may be simply transported bythe jet to region 38 where they form a deposit on the substrate. Theresult would be analogous to that of other evaporation coatingtechniques in use today. In other applications, however, it may bedesirable to cause these evaporated species to suffer further reactionsin order to synthesize the desired depositing species.

A specific advantage of the process and apparatus of my invention isthat any precursor species which has successfully been introduced as acomponent in mixture with the carrier gas may be acted upon further inorder to synthesize a depositing species. This action may take the formof:

1) Chemical reaction with another species

2) Dissociation of the chemical species by pyrolysis at a heated solidsurface

3) Dissociation of a similar species by absorption of radiation(photochemistry).

4) Dissociation due to interaction with a plasma or discharge (archeating)

5) A combination of these methods acting on one or more speciesintroduced by one or more delivery mechanisms.

This wide variety of actions is possible in my invention, preciselybecause the transport of the highly reactive, saturated depositingspecies by a jet of carrier gas serves to spatially isolate thesynthesis chemical reactions from the actual condensation reaction atthe substrate surface. Thus the thermodynamic and gasdynamic flowconditions (as well as other conditions, e.g. radiation intensity)governing the behavior of the chemically reacting gas mixture may bevaried widely on either end of the jet in order to independentlyoptimize both the synthesis reaction and the condensation reaction.Naturally, the flow conditions at the beginning of the jet (site ofinitiation of depositing species synthesis reactions) are coupled to theconditions at the surface of the substrate at the end of the jet (siteof condensation reaction to form a network solid). But although thisdependence is very complicated it may be controlled by altering the flowgeometry, gas pressure, temperature, mixture concentration, etc. asdescribed below.

Once the synthesis reaction is started, it may continue as the reactantspecies are transported in the jet. Indeed as the carrier gas expandsthrough the nozzle, it converts its thermal energy into mechanicalenergy and cools. The expanding carrier gas also cools the reactants,and provides a "heat sink" for any exothermic reactions which may occur.These continuing reactions (including homogenous nucleation) will dependon the evolving thermodynamic conditions of the flow as the gas mixtureexpands through the nozzle and forms the jet. The conditions aredependant on the expansion rate which is largely controlled by thenozzle geometry. (One of ordinary skill in the art reading thisdisclosure will perhaps have need of further background in the gasdynamics of nozzle flows. For this purpose, reference may be had to J.D. Anderson, Jr., Modern Compressible Flow, 1982 McGraw-Hill, New Yorkor H. W. Liepmann and A. Roshko, Elements of Gas-Dynamics, 1957 J.Wiley, New York, which are specifically incorporated herein byreference.) A diverging section may be added to the nozzle to controlthe expansion rate before the flow exits the nozzle to form a free jet.Indeed the addition of a diverging section can change the nucleationrate by several orders of magnitude. (Again, for purposes of referencefor those of ordinary skill in the art who may require furtherbackground in gas-phase nucleation of clusters in seeded molecularbeams, the reader is referred to O. Abraham, et al, "Gasdynamics of VerySmall Laval Nozzles", Physics of Fluids 224 (6), 1981 American Instituteof Physics; and O. F. Hagena "Cluster Beams from Nozzle Sources",Gasdynamics vol. 4, 1974 Marcel Dekker, New York, which are specificallyincorporated herein by reference.)

2. Transport of Depositing Species.

Once the synthesis step is initiated (synthesis can continue while thereactants are being transported) the transport step is achieved alwaysin the same manner. The high speed flow of the carrier gas entrains thedepositing molecules and convects them into the flow region 38 whichborders on the object to be coated. In certain respects, the flow fieldwill be largely dominated by the behavior of the inert carrier fluid,since the reactant molecules are present in dilute concentration (oforder 1 molar % or less). One can analyze the flow as if it were thejust pure carrier fluid under the same flow conditions and then byexamining the degree to which the molecules of the depositing speciesare "entrained" in the flow of the carrier gas. This becomes a questionof whether the species being transported is in equilibrium with thecarrier gas. As we shall see, this question of equilibrium (ordisequilibrium) is also very important in determining the exactmechanism of deposition.

Differences in the mixtures flow field as compared to that of the purecarrier fluid under the same fluid dynamic conditions will be mainly dueto the possible disparity in masses of the mixtures constituentmolecules and also due to the energy addition or consumption caused bythe synthesis reactions. If one chooses to use a carrier gas with anespecially small molecular weight (e.g. hydrogen or helium) then mostdepositing species will have a molecular weight which is one or severalorders of magnitude greater (e.g. many metal or metal-oxide radicals).The possibility of dimerization, trimerization and ultimately clusternucleation will increase this mass disparity, and with significantclustering the distinction between considering the behavior of thedepositing species as that of molecules or as aerosol particles becomesless precise. In any event, even if the depositing species is present asonly about one percent of the mixtures component molecules, its mass,momentum and energy--as distinct from that of the carrier fluid--may befar from negligible. In fact, it was the study of the behavior of heavymolecules in the high speed flow of a light bath which, inspired theinvention of this deposition technique.

Accordingly, it will be found profitable in the case of a disparate massmixture to exploit the similarity with aerosols when trying to model themotion of the heavy species. Even when the depositing species isdistinctly molecular, rather than aerosol, the inertial effectsgoverning its behavior can be highly significant. (One of ordinary skillin the art reading this disclosure will perhaps have need of furtherbackground in the gasdynamics of disparate mass mixtures, and inparticular velocity persistance effects. For this purpose reference maybe had to: J. Fernandez de la Mora, "Inertial Nonequilibrium in StronglyDecelerated Gas Mixtures of Disparate Molecular Weights", PhysicalReview A 25 (2), 1982 The American Physical Society; or J. Fernandez dela Mora, "Simplified Kinetic Treatment of Heavy Molecule VelocityPersistance Effects; Application to Species Separation", From RarifiedGas Dynamics, Vol. 74 of Progress in Astronautics and Aeronautics, 1981American Institute of Aeronautics and Astronautics--both of which areincorporated herein by reference.) In our high speed flow regime, theheavy depositing species can be in a state of extreme disequilibriumwith the carrier fluid, so the conventional theory of continuummechanics is not always applicable. However, since the heavy depositingspecies represents such a small fraction of the mixture's molecules, themixture's flow can be treated as outlined previously: first observe orestimate from theory the flow field of the pure carrier gas, thendetermine the degree to which the heavy molecules "lag" behind the flowof the carrier.

The presence of the depositing species in dilute concentration will nothinder the flow of the carrier significantly, so the carrier flow fieldcan be treated in the conventional manner. Such a treatment will resultin the gasdynamic knowledge of the jet of the carrier fluid whichcompletely depends on the following parameters:

1) Initial (stagnation) pressure

2) Initial (stagnation) temperature

3) Nozzle Geometry

4) Ratio between the initial and downstream pressures (from nozzle exit)

5) Gas viscosity

6) Ratio of the carrier gas, specific heats, one at constant pressure,the other at constant volume.

As result of my described process and apparatus, it will now berecognized that for a given choice of carrier gas and depositingspecies, parameters 1, 2, 3 and 4 can be independently varied, radicallyaltering the flow field, which in turn will alter the transport anddeposition.

The motion of the depositing species will depend completely on the MachNumber (nondimensional speed) of the carrier flow field and the StokesNumber; this latter parameter will be a measure of the "lag" of theheavy depositing molecules behind the flow of the carrier fluid. Suchlagging is often termed "velocity persistance" or "inertia" anddescribes departures from the motion of the molecules predicted bycontinuum mechanics. In this way, the Stokes Number represents thedegree to which the heavy depositing species is in dynamicaldisequilibrium with the carrier bath. Thus with the knowledge of thecarrier gas flow field which is easily determined through wellestablished theory, and an accurate estimation of the velocity la# ofthe depositing species in that flow field one can determine and controlthe transport of the depositing species.

Now the general representation of the flow velocity is the Mach Number(M), a nondimensional gasdynamic parameter which is defined as the ratioof magnitude of the flow velocity (U) to the gas' thermal speed (C)

    M.tbd.U/C                                                  (1)

We consider now the steady state of deposition, in which the flowregime, synthesis and deposition reactions are established, and continueunchanged until the desired, thin film thickness is achieved. In steadystate, the flow field remains constant through time, and this simplifiesthe theoretical treatment. For the given geometry the flow field is thencalculated assuming that the carrier gas is pure and employingconventional continuum mechanics. Depending on the application, theoptimal flow field may be subsonic or supersonic. For any gas flowingthrough a nozzle at fairly large Reynolds Number, a pressure ratioacross the nozzle (i.e. the quantity P_(i) /P_(b) where P_(i) is the gaspressure upstream of the nozzle, and P_(b) is the base pressure in thedeposition chamber) of between unity (1) and approximately two (2) (foralmost any gas) will correspond to subsonic flow whereas pressure ratiosgreater than about two (2) will cause supersonic flow. Naturally, alarger pressure ratio requires greater pumping capacity to maintain theflow. (In experiments, the flow Mach Number has ranged from one-tenth(0.1) to about unity (1).) The carrier gas used most often has beenhelium which has a sound speed at room temperature of about a kilometerper second. Since the distance over which the depositing species wastransported was at most a few centimeters, the transport obviouslyhappens very quickly.)

With knowledge of the carrier gas' flow field, one can begin anestimation of the Stokes Number. To reiterate, the Stokes Number is ameasure of the degree to which the molecules of the depositing species"lag" behind the high speed motion of the carrier gas molecules. Forexample, if a molecule to be deposited originates in a solid filamentplaced in region R1 of the flow field and is then evaporated off intothe gas flow, it must be accelerated from a state in which it isessentially at rest to the speed of the surrounding gas flow. Thisacceleration takes a certain time, and the Stokes Number is, in acertain sense, a measure of that time.

The Stokes Number (S) is actually a ratio of two times: 1) themicroscopic particle relaxation time (τ) and 2) the overall macroscopicacceleration time of the flow (t).

    S.tbd.τ/t                                              (2)

The relaxation time is the average time required for the molecules ofthe depositing species to achieve velocity equilibrium with the hostfluid. Equilibrium in gases arises from collisions between theirconstituent molecules. For example if a molecule is moving at a velocityradically different from the mean velocity of all the other molecules ina gas (i.e. if it is in disequilibrium) , collisions cause a transfer ofenergy and momentum between molecules, which serve to bring the velocityof the unusual molecule more in line with the mean flow velocity. Itshould be emphasized that the relaxation time is a statisticalprobability and only has meaning for a large number of molecules.Collisions between molecules of similar masses are very effective intransferring energy and momentum, so perhaps only one collision isnecessary to relax a molecule in a gas of other molecules with equalmass. However the transfer of energy and momentum from a heavy particleto a light particle is relatively inefficient, hence many collisions arenecessary to equilibrate a heavy molecule with a gas of lightermolecules. These collisions take time, of course, so the more collisionsnecessary, the greater the relaxation time (τ).

Naturally, there are also collisions between the molecules of thedepositing species but since their concentration in mixture is so small,their number density is very small, so collisions are much lessfrequent. (In fact, in the absence of the carrier molecules, thedensities of the depositing species would correspond to flow in theextremely rarified regime treated in hypersonic theory.) Actually thefrequency of these self collisions of the depositing species will beimportant in determining the synthesis reaction, nucleation and, to acertain extent, the deposition rates, but for the present we areconcerned with the degree to which the depositing species moleculesachieve equilibration with the carrier gas. From statistical mechanicsone can approximate the relaxation time (t) through Einstein's formula:

    r.tbd.m.sub.d D/(k.sub.B T)                                (3)

where: m_(d) .tbd.Molecular weight of depositing species

D.tbd.Diffusion coefficient (depositing in carrier)

k_(B) .tbd.Boltzmann's constant

T.tbd.Absolute Temperature

The diffusion coefficient can be measured in a standard experiment or itmay be estimated using the Chapman-Enskog theory. (One of ordinary skillin the art on reading this disclosure may require a greater backgroundin gas-phase mass transport theory. For this purpose, reference may behad to: D. E. Rosner, Introduction to Energy, Mass and MomentumTransport in Chemically Reacting Fluids, (in press) 1984 J.Wiley--EXXON, 1984 New York--which is specifically incorporated hereinby reference.) Thus, (t) is easily calculable from known quantities.

The other time which appears in the definition of the Stokes Number(Equation 2) is the fluid flow's macroscopic time of acceleration (t).To determine this time, one chooses a characteristic length of the flowgeometry (d) (e.g. the nozzle throat diameter) and the average flowvelocity (U) over that length. One obtains (t) from the followingrelation:

    t=d/U                                                      (4)

The choice of (d) is rather subjective, and so one must carefully choosethe most relevant distance. Combining Equations 2, 3 and 4 we have:

    S=m.sub.d DUρ/(dk.sub.B T)                             (5)

or one may choose to exploit the perfect gas law to write this as:

    s=m.sub.d DUp/(dm.sub.C P)                                 (6)

where: ρ.tbd.carrier gas density

m_(c) .tbd.carrier gas molecular weight

P.tbd.m gas pressure

In an equilibrium situation, the Stokes Number is very small comparedwith unity, and this corresponds to the fact that in equilibrium, themolecular relaxation occurs much faster than the changes in the overallflow velocity. However, note that Equation 6 indicates that an increasein the ratio (m_(d) /m_(c)) of the depositing species to the carrierfluid's molecular weight will increase the Stokes Number. In fact, ifthis ratio is of order one hundred, it is possible to reach StokesNumbers near unity even in subsonic flows. A Stokes Number near unitycorresponds to conditions of extreme disequilibrium, where the inertiaof the heavy species is so large as to dominate over the viscous forcesof the carrier fluid. These inertial effects cause the depositingspecies to become disentrained from the flow of the accelerating carrierfluid and to pursue their own independent, ballistic-like trajectories.This inertial behavior is analogous to the behavior of macroscopicaerosol particles in disequilibrium with their carrier fluid. Thenovelty is in noting that such effects are also observable in massivemolecules. To first order such effects account for behavior of heavyspecies normally attributed to "pressure diffusion".

Now with a knowledge of the carrier fluid flow field and the StokesNumber one can account for the transport of the depositing species. Toachieve the transport, the condensing species must be entrained in theflow of the carrier; and to maximize this entrainment one must minimizethe Stokes Number. Thus for a given depositing species this would implya choice of carrier gas with similar molecular weight. However, as weshall see in the next subsection of this document which describes thedeposition step, a regime of high Stokes Number may be desirable at theend of the transport step, so in certain applications it may be highlydesirable to choose a carrier gas of much lower molecular mass to thatof the depositing species.

The Mach Number (i.e. flow velocity), Stokes Number, and thus thetransport will depend completely on the following parameters:

1) Initial pressure

2) Initial temperature

3) Pressure ratio (across nozzle)

4) Nozzle geometry

5) Concentration of minority species

6) Mass ratio (depositing to carrier species)

7) Diffusion coefficient (depositing species in carrier)

8) Carrier gas viscosity

9) Specific heat ratio of carrier gas

Again, when one employs my process for a given choice of depositingspecies and carrier fluid, parameter i through 5 can be variedindependently. As one of my preferred embodiments the Nozzle Geometryshould be designed as described below so that even when one is using adisparate mass mixture the depositing species is efficiently entrainedin the carrier fluid during acceleration. Such a disparate mass mixture,then allows one to employ inertial effects to achieve deposition (adescription of this follows shortly). This nozzle design varies with thespecific chemical application and is done using the Navier-Stokes fluidmechanics mathematical model as described below. Refer to the throatsection of the nozzle to describe the upstream portion of the flowregion 34 in which the synthesis reactions occur. When a condensiblespecies is caused to be formed near the centerline of the flow throughthe nozzle (e.g. from evaporation off a filament placed there), thisspecies will begin to diffuse outward toward the solid walls of thenozzle but it will also experience collisions with the molecules of theflowing carrier gas which will convect it downstream. The enclosed areadepicts the region R1 populated by the condensible species as theydiffuse outward from the incipient jet's axis while being transporteddownstream. Optimal circumstances are such that the condensible speciesis convected past the nozzle exit before diffusion to the nozzle'sthroat's walls can occur, so condensation on the nozzle itself isavoided. The advantage in placing the filament upstream from the nozzlethroat is that the depositing species is accelerated along with thecarrier bath, so the entrainment is enhanced. Other geometries withdiffering transport properties are possible.

In practice, as described below successful transport of a given speciesmay be achieved over a wide range of flow rates (i.e. pressure ratiosP_(i) /P_(b)), so this allows variation of the thermodynamic andgasdynamic conditions within this range to optimize the synthesisreactions. Observe that Equation 6 implies that increasing the carrierpressure reduces the Stokes Number and thereby increases the entrainmentrate. If all else remains constant, then by increasing the pressureratio, one will increase the flow rate, and thus the transport rate.Furthermore, by adjusting the position at which the synthesis reactionbegins (e.g. by changing the placement of the filament in evaporation)and/or by changing the placement of the object to be coated, one cancontrol the overall residence time of the depositing species in thegas-phase of the jet. This control of the residence time along with thewide latitude in setting the concentrations can be used to govern thesynthesis reactions. Also one can merely change the concentrations ofthe reacting species in order to alter the synthesis reactions.Naturally, for a given depositing species, one is free to choose anyinert carrier fluid, which choice will depend on criteria peculiar tothat application. These many degrees of freedom, afford greatflexibility in designing an apparatus intended to cause a particulardeposition to occur. Each envisioned application will require asystematic variation of these parameters to find the optimalconfiguration.

The analysis of the transport process is complicated by the very factthat the synthesis reactions may continue to occur during the transport.Consequently, as experiments have demonstrated a slight change in theapparatus' geometry can have a profound effect on the gas phaseresidence time of the reactants, which, in turn, will greatly alter theproducts of the reaction. The addition of a diverging section on thenozzle will afford control over the gas expansion rate, which is notavailable in the case of the free jet. Such a section has been shown tochange the nucleation rate of a seeded species by many orders ofmagnitude. Thus, a diverging section could provide another means ofcontrol over the synthesis reaction and the transport rates.

Unfortunately, it has been recognized in gasdynamics that theoreticaland experimental determinations of the degree of clustering are verydifficult. But often, if clustering is extensive, a particulatestructure will persist in the morphology of the deposit. Whether this isdesirable or not will depend on the given application (it would be in,say, the deposition of a catalytic material, since that catalysis maybenefit from the increased surface area of a catalytic material with aparticulate structure).

The important point is that this phenomenon may be controlled to a largedegree. (A treatment of the means of control is given in below.) Thus,the synthesis and transport steps--which as noted, can occursimultaneously--are achieved. They are the preliminary steps in theoverall deposition reaction.

3) Deposition and Film Growth.

Once the depositing species is synthesized and convected into the regionR2 of the flow field, its molecules migrate to the substrates surfacealternately or in relative combination through one of the following twomechanisms.

1) Molecular Diffusion

2) Inertial Impaction

Which mechanism dominates in an actual deposition will depend on theStokes Number of the flow. As the gas mixture expands through the nozzleit forms a jet. When this jet encounters the object to be coated, whichhas been placed in the region 38 of the flow field, the gas flow willdecelerate. There arises again a situation of changing flow velocity,and the possibility of "velocity persistence" for the depositing speciesif there is a significant mass disparity. This possibility will bespecified by the Stokes Number.

In addition to a flat substrate 50, FIG. 6, an object to be coated (i.e.the substrate) may be a "bluff body" 52, FIG. 7 or it may have a "sharp"edge including "wedges", 54, FIG. 8 "cones" and "cylinders" 56, FIG. 9of small diameter compared to the jet diameters,) The flow past suchgenerally characterized bodies can be calculated on the basis of thedocumentation which is found in many texts on the theory of fluiddynamics for both the subsonic and supersonic cases. (One of ordinaryskill in the art on reading this disclosure perhaps requires furtherbackground in the theory of fluid flow past solid bodies. For thispurpose, reference may be had to: G. K. Batchelor, An Introduction toFluid Dynamics, 1967 Cambridge University Press, Great Britain--which isspecifically incorporated herein by reference.) The case of subsonicflow impinging on a bluff body will be treated first, and then the casesof the sharp edge and supersonic flow.

The jet impingement on a blunt body can be likened to the so called"stagnation point" flow and, in fact, the deposition will beconcentrated around the stagnation point. If the object has a breadthwhich is an order of magnitude larger than the jet diameter--which is ofcourse comparable to the nozzle orifice diameter--then it should beconsidered as a bluff planar body with breadth which is essentiallyinfinitely large in comparison to the jet width. Even if the object isnot actually planar, the theory is still applicable as long as its shapehas fairly small curvature in comparison to the jet's width.

The jet transports the depositing species near the surface of thesubstrate. When the Stokes Number is sufficiently small, that is if thejet's speed is fairly slow or if the carrier fluid has a molecularweight comparable to that of the depositing species or if the pressureis high enough (see Equation 6), then continuum mechanics will reign;the mixture can be considered in equilibrium; and diffusion willdominate the deposition process. The jet will convect the condensingspecies near the substrate's surface, and because the flow speed willthen have slowed, there will be sufficient time for molecular diffusionto this surface. Since the depositing species can condense on thesurface, the substrate will "capture" this species from the gas-phaseand a solid deposit will form. The substrate acts like a mass "sink" forthe condensing species--at least in the sense that said species is agas-phase species. But since the depositing species is removed from thegas-phase, its concentration in the gas mixture is depleted in theportion of the flow field abutting the substrate surface (this flowregion is termed 38). This, of course, causes a spatial concentrationgradient which drives further gas-phase diffusion in the mixture of thedepositing species. toward the substrate surface. This process continuesas the gas flows along the "infinite" breadth of the "bluff body"substrate and essentially all of the depositing species condenses fromthe gas-phase. Thus, nearly all of the synthesized depositing speciescondenses into thin film form. The carrier gas exits the depositionchamber downstream, and convects along with it any of the reactantspecies remaining in the gas-phase which were not fully consumed in thesynthesis reactions producing the condensible species. However, if thecarrier gas is recirculated via the recirculation loop, then thesereactant species are also recycled and they are reintroduced in the flowthrough the nozzle and into the flow region R1 where they again have achance of being consumed in the continuing synthesis reactions. So evenwhen a specific preferred embodiment involves the fabrication of a thinfilm using a deposition process which includes a chemical synthesisreaction step that is only fractionally efficient in converting thegas-phase reaction precursors into the desired depositing species, thereis still high efficiency in the use of materials because the unreactedgas-phase species can easily be recovered and recycled. Thus myinvention of method and apparatus for depositing thin films is highlyefficient in that it converts nearly all of the initial raw chemicalsinto the desired thin film material.

The alternate deposition mechanism occurs when the Stokes Number of theflow is large; but even when inertial impaction is the dominantmechanism, diffusion still insures that all of the depositing speciescondenses--even that small portion of the depositing species' molecularpopulation with insufficient velocity to be inertially impacted. Thetreatment of inertial impaction will begin with a discussion of the mostimportant aspect of this phenomenon as it affects the condensationreaction: the unusually high kinetic energies of the depositing speciesmolecules in the case where there is significant disparity in themolecular masses (i.e. m_(d) /m_(c) is large), and the flow speed isfast. This large energy can affect the chemical reactions at thesubstrate surface as the heavy species collides with the atoms of thesurface. (One of ordinary skill in the art on reading this disclosureperhaps require further background in the field of surface impactchemistry. For this purpose, reference may be had to: M. S. Connolly, etal, "Activation of Chemical Reaction by Impact of Molecules on aSurface", Journal of Physical Chemistry 85 (3), 1981 American ChemicalSociety; or E. Kolodney, et al, "Collision Induced Dissociation ofMolecular Iodine on Sapphire", Journal of Chemical Physics 79 (9), 1983American Institute of Physics--which are both specifically incorporatedherein by reference.) Consider the expansion of the carrier gas. Beforethe expansion begins, the carrier gas has enthalpy (H) given by:

    H=k.sub.B T.sub.i γ/(γ-1)                      (7)

where: γ.tbd.specific heat ratio of carrier gas

k_(B) .tbd.Boltzmann's constant

T_(i) .tbd.Initial (stagnation) absolute temperature

Since the factor (γ/γ-1) depends on the gas, but is always of orderunity, the enthalpy is always of order (k_(B) T_(i)). If the expansionoccurs into a region that has been largely evacuated, this enthalpy willbe mostly converted to kinetic energy of the light gas flow (K).

    K=(m.sub.c /2)U.sup.2 ≈H                           (8)

where: m_(c) =molecular weight of carrier

U=Flow velocity

Provided the expansion has proceeded at a rate slow enough so that theStokes Number has remained low, the heavy molecules of the depositingspecies dispersed in the flow will be efficiently entrained and willtherefore share this velocity (U) and have their own kinetic energy,(K_(d)) which is defined as:

    K.sub.d .tbd.(m.sub.d /2)U.sup.2 ≈(m.sub.d /m.sub.c)H(9)

where: m_(d) .tbd.molecular mass of depositing species.

As previously observed, the mass ratio can be of order 100, so thekinetic energy of the heavy species can be unusually high, much greaterthan its initial thermal energy. Even when the flow remains subsonic,such a heavy species may have a kinetic energy of several electron voltsper molecule, provided the Mach Number is high (although less than 1)and the heavy molecules have been adequately entrained. When thismechanical energy of the depositing species is very large, its initialthermal energy may be an insignificant fraction of its total energy sothe molecules can be highly monoenergenetic. (One of ordinary skill inthe art on reading this disclosure may require further background in theflow energies of nozzle beams--particularly in the energy distributionamong the population of heavy molecules seeded in the flow of a lightgas. For this purpose, reference may be had to: J. B. Anderson,"Molecular Beams from Nozzle Sources", Gasdynamics, Vol. 4, 1974 MarcelDekker, New York.) High velocity also means very high momentum for theheavy molecules; from this arises the inertial effects.

An important feature of the stagnation point is that the continuum flowactually has zero flow velocity there. Naturally, the gas cannot have avelocity perpendicular to the flat plate, directly at the flat plate,but also the gas' finite viscosity insures that there is no lateral flowof gas in the layer of fluid immediately next to the plate. This is theso called "no slip condition" for Newtonian fluids. These features implythat the flow in the immediate region of the stagnation point is veryslow. Now as the depositing species is accelerated through the nozzle inhigh Mach Number flow, it will have a velocity comparable to the speedof sound of the carrier fluid which is of order one kilometer per secondfor light gases like helium or hydrogen at room temperature. When thejet then encounters the stagnation point region, the flow mustdecelerate to near zero velocity (zero at the solid surface). Obviously,regimes of extremely high deceleration can be set up in the flow field.If the Stokes Number is then large enough (since it is proportional tothe acceleration), the viscous forces of the carrier fluid may not beadequately large to maintain the heavy molecules in the continuumregime. They become disentrained from the carrier's continuum flow andpursue independent trajectories, encountering the plate at finitevelocities, where they impact to form the deposit. The behavior isanalogous to the what has been called inertial impaction of aerosolparticles. (One of ordinary skill in the art may on reading thisdisclosure may require further background in the field of aerosolphysics. For this purpose, reference may be had to: D. T. Shaw RecentDevelopments in Aerosol Science, 1978 J. Wiley, New York--which isincorporated herein specifically by reference.)

The deposition process should be viewed as a heterogeneous chemicalreaction. As previously observed, when the depositing species isinertially impacted, its large amount of kinetic energy can play animportant role in this condensation reaction. Indeed with supersonicflow velocities, a stable species can be caused to dissociate solelythrough the collision energy of impaction. A change in flow velocity canalter the energy of impaction, which in turn markedly affects theheterogeneous reaction and the qualities of the thin film therebyproduced. As stated previously, changes in the flow velocity and in theconcentration (partial pressure) of the reactant species can affect thesynthesis reactions; however, if one assumes that the identity of thedepositing species remains constant. these parameters (through theirgovernance of the rates at which the depositing species molecules areintroduced at the substrate surface and the their kinetic energies) aswell as the substrate temperature are the main variables governing thecondensation chemical reaction.

These variables can, of course, be controlled, and there is greatlatitude in setting them so it is possible that many useful depositionreactions, each of which would proceed optimally at specific conditionswithin this wide range of possible conditions, could be induced tooccur.

This theory can be extended to the case of sharp edged substrates. For a"wedge" or "cone" oriented so that its sharp edge is directed into theflow of the jet, the stagnation point will occur on that edge (even avery sharp edge is blunt on a molecular scale). Any inertial impactionwill occur on or near the sharp edge only, however viscosity will slowthe flow past the wedge's sides, so the deposition due to moleculardiffusion will occur on these sides. The relative importance of each ofthese mechanisms will depend on the flow speed, identity of the carrierand depositing species, and the specific flow geometry.

In case of a "cylinder" or "sphere" with diameter smaller than thediameter of the jet, impaction will be the only mechanism at high speed,and will occur on the upstream surface where again there is a stagnationpoint; whereas at low speed diffusion will allow condensation on areasof the substrate surfaces further downstream. However, since thesubstrate is of comparable size to the jet width, diffusion will notinsure that all of the depositing species molecules will encounter thesubstrate and deposit. Some molecules will "miss" and be convecteddownstream.

These concepts apply as well to the supersonic case. The highest heavyspecies kinetic energies can be achieved in this case, which can be oforder ten electron volts per molecule. Such high energies are notpossible with conventional Chemical Vapor Deposition, or EvaporativeCoating Processes and they are achieved in a low vacuum environment incontrast to the high vacuums required of Sputtering, conventionalEvaporative Coating and other deposition technologies. In the supersoniccase, one must be aware that detached shocks will form before bluntobjects placed in region R2 while attached shocks form on sharp edgedobjects. In the latter case, a heavy depositing species will be impactedwith highest energy at the point of the shock attachment (the sharp edgeitself), otherwise the flow is decelerated through the shock so thedepositing species will lose some of its high free stream velocity. Inthe case of the detached shock, the best choice of characteristic length(d) for calculating the Stokes Number (see Equations 4 and 6) of theflow is the shock to object distance.

In summary, my preferred deposition process embodies the disclosed threesteps:

1) Synthesis of depositing species

2) Transport of said species

3) Deposition and film growth

The deposition process may be viewed as one long steady state, gas-phasechemical reaction which begins with the reaction that synthesizes thedepositing species, and ends as that species forms a deposit in thecondensation reaction. The latter reaction is heterogenous and resultsin the formation of a network solid with chemical bonding to thesubstrate surface. The means of controlling the evolving chemicalreactions is now described.

A benefit of using the carrier fluid mechanism of transport is thatdominant flow of the inert carrier serves to purge the apparatus of gasphase impurities; thus control of the deposition chamber atmosphere isachieved. Specifically, before deposition begins, the flow of the purecarrier fluid is established through the apparatus. Any unwanted speciesintroduced into the interior of the vacuum system (while it may havebeen open to the ambient atmosphere) will be entrained in the carrierflow and convected out. Provided there are no leaks no the apparatus,the flow will be of the pure carrier fluid. (The flow is presumed tooriginate from a storage chamber charged with a supply of highlypurified inert gas.) Next, the flow of the reactants is established andthe deposition reaction initiated. In this manner, the identity of thespecies involved in the synthesis and deposition reactants iscontrolled.

Even if there are small leaks in the deposition chamber's walls, thecarrier gas flows between the substrate and these walls and presentssomewhat of a dynamic barrier which isolates the deposition reactionfrom these possible sources of impurities. In other words, the fastcarrier gas flow convects the atmospheric impurities (or impurities dueto outgassing of the chamber's solid surfaces) downstream before thereis time for them to diffuse across the flow to the substrate.(Naturally, this effect will be strongly dependent on the size andposition of the leak in the system.) Futhermore, it is conceivable thatthe entire deposition could occur in a system with carrier gas pressurealways higher than atmospheric pressure. Thus, any leaks would leak out.There are no fundamental theoretical reasons which would preclude thisconcept, however the enormous pumps needed to operate at such highpressures--and therefore such high mass flux--have not been availablefor use in a laboratory demonstration. (Naturally, in practice theeconomic costs of operating such pumps must balanced against thebenefits of a high pressure process.) In any event, the predominant flowof inert carrier serves to purge the apparatus initially and to maintaina controlled atmosphere for deposition. Thus the only species presentare the inert carrier and the reactant species. Their relativeconcentrations can be varied provided the total number density of thereactants remains small compared to that of the carrier. Depending onthe degree to which they are in equilibrium with the carrier fluid, thereactants partial pressures and temperatures will be determined by thepressure and temperature of the carrier gas , which depend throughoutthe flow field on their initial values before the expansion (P_(i) andT_(i)), on the nozzle's (variable) geometry, and on the flow pressureratio (P_(i) /P_(b) ' where P_(b) is the background pressure in thedeposition chamber). These parameters will control the velocity,pressure and temperature fields throughout the flow field (assumingnegligible energy addition or consumption due to the synthesisreactions) and thus these latter thermodynamic conditions which governthe chemistry of the process can be manipulated to optimize theenvisioned synthesis and condensation reactions. Anomalies due todisequilibrium in the gas mixture, or those caused by non-negligibleenergy transfer to or from the flow, can be estimated using the StokesNumber, along with other standard techniques employed in the theory ofmass and energy transport in chemically reacting fluid flows.

In a flowing chemically reacting fluid under steady state conditions,the reactions occur over distance; the time of the reaction is the timeneeded for the flow to convect the reactants over the distance andthrough the reaction. Thus the flow field not only determines theenergetics of the reaction; the velocity field and apparatus' geometry(e.g. the nozzle to substrate distance, or length of the free jet.) willalso determine the residence time of the reactant species in thegas-phase, and therefore the time of the reaction. More precisely, theconcentration, self collision time, and residence time of the reactantswill specify their probability of interaction. This probability alongwith the energy of this molecular interaction will determine thesynthesis reactions. Both probability and energy can be largelycontrolled in this system through the following macroscopic variables.

1) Choice of carrier gas

2) Apparatus Geometry

3) Mixture concentration

4) Mixture initial pressure

5) Mixture initial temperature

6) Base pressure in deposition chamber.

Through these variables the system affords control over the synthesisreaction. The optimal conditions will depend on each application.

The deposition reaction can also be largely controlled by setting thesubstrate temperature, and the energy of the depositing molecules. Bycontrolling the substrate temperature, one can control the thermal"history" of the thin film solid being formed. The rate of quench isextremely important in determining the properties of the product solidphase material. When the flowing carrier fluid and depositing speciesare in equilibrium, the energy of the depositing molecules as theyencounter the substrate surface will be determined by the flowtemperature, but in the case of extreme disequilibrium under whichinertial impaction can occur, the depositing molecules may encounter thesubstrate with very large transnational energy (as discussedpreviously), which will, of course, affect the deposition reaction.

As previously stated, the degree of disequilibrium can be represented bythe Stokes Number. To calculate precisely the distance (d) over whichthe deceleration of the jet occurs before impaction--and which (d)appears in the Equation (6), defining the Stokes Number--one must solvethe Navier--Stokes equations governing the flow. This is a relativelycomplicated task. However, for many geometries one could borrow from thedeveloped theory of aerosol impactor design. (One of ordinary skill inthe art on reading this disclosure may have need of further backgroundin the field of aerosol impactors. For this purpose reference can bemade to: K. Willeke, et al, "The Influence of Flow Entry and CollectingSurface on the Performance of Inertial Impactors", Journal of Colloidand Interface Science 53 (i), 1983 American Institute of Physics; and V.A. Marple, et al., "Impactor Design", Atmospheric Environment 10, 1976Pergamon Press, Great Britain--which are both incorporated hereinspecifically by reference). Marple, et al, note that (d) should beequated with the hydraulic diameter of the free jet. (For a circularorifice, the hydraulic diameter is merely the orifice diameter, whilefor a rectangular orifice, the hydraulic diameter is one half of theorifice width.) This conclusion is only valid at high Reynolds Numberflow and only if there is enough distance between the nozzle exit andthe substrate for a subsonic jet to develop. The latter condition issatisfied provided the that distance is greater than the nozzleorifice's characteristic width. Following the development in Marple'swork one would employ the free jet velocity (U) as the velocity inEquation (6). (The velocity of the free jet can be calculated using thestandard theory of continuum mechanics, assuming that the gas is onlycomposed of the pure carrier fluid.) Here one must assume that a heavyspecies shares this velocity with the light gas, or in other words doesnot "lag".

For the heavy species to be in equilibrium within the free jet of lightcarrier, they must be efficiently entrained in the accelerating flow ofthe carrier through the nozzle. To insure this the nozzle must bedesigned to minimize the Stokes Number in the accelerating part of theflow. Rather than solving the complete Navier-Stokes Equations of theaccelerating flow (as Willeke, et al and Marple, et al, have done) onecan begin with the standard one dimensional approximation of the carrierflow through the nozzle. (Again see J. D. Anderson, Jr., ModernCompressible Flow, as cited previously.) One approximates the flowvelocity as the component of the velocity along the axis of the nozzle,calling this the X - coordinate, while neglecting the other components.The flow velocity (U) is a scaler in this approximation and for a givenmass flux will completely depend on the nozzle geometry. Specifically,the flow velocity (U) at a position (X) will be inversely proportionalto the cross sectional area (A) of the nozzle duct through which theflow must pass at that position. This is a simple consequence of massconservation and so (U) as a function of (X) will depend on (A) as afunction of (X) (i.e. the velocity depends on the nozzle geometry). Onecan define a local Stokes Number:

    S=τ(dU/dX)                                             (10)

where: dU/dX.tbd.the spatial gradient of U.

And by requiring the accelerating part of the flow field to be one inwhich dU/dX is minimized, the Stokes Number is also minimized. Thiswill, in turn, establish (A) as a function of (X) thereby specifying thenozzle's geometry. (It must be remembered that only if S<<1, will thedepositing species be in equilibrium and therefore adequatelyentrained.) In practice, one must compromise between minimizing theacceleration Stokes Number, and maximizing the deceleration StokesNumber to achieve inertial impaction of a species. Each application willhave its own specific requirements. Of course, these requirements mustalso be balanced against optimizing the flow conditions to achieveproper synthesis of the depositing species. All of these variables willdepend on the desired application.

In addition, each application will dictate the choice of nozzlegeometry, and choice of substrate shape and material. All experimentaldemonstrations were performed with a conical nozzle, but for coating abroad area, a rectangular nozzle, (with one long dimension) may beemployed. To coat a large area, the substrate may be moved through thejet. Although the condensation of the depositing species is concentratedat the stagnation point, this point (or line in the case of arectangular nozzle) is moved across the substrate's surface, so that thedeposition also occurs across the entire surface. The rate of motionwill determine the thickness and evenness (discounting edge effects) ofthe thin film deposit so produced.

In practice, the substrates may be coated in a "batch" mode in which thedeposition chamber is "charged" with many individual substrates, beforeit is sealed from the atmosphere, and then a mechanism positions eachindividual substrate under the jet to receive its thin film coating asthe depositing species is convected to it and condenses on it.Alternately, for rolled or coiled stock as substrate material, thedeposition may occur in a "semi-continuous" mode, in which thedeposition chamber is charged with a "spool" of substrate material 58,FIG. 10. This material is continuously "unwound" and passed through thejet, and wound onto another "spool" positioned to receive it. Thesubstrate material receives its thin film deposit at the stagnationpoint where the jet impinges on it. At the stagnation point, thedepositing species condenses. The final product is a roll or coil ofcoated material. The entire apparatus is contained within the depositionchamber previously described, and is substituted for the generalizedsubstrate previously described.

True continuous deposition could be achieved if the deposition chamberwere open to the atmosphere. This would require maintenance of thepressure in this chamber at slightly above the ambient pressure so thatsome carrier gas could flow out the open ports and insure that noatmospheric species could diffuse inward. A gas gauging mechanism couldmaintain the control of the chamber atmosphere. Of course, if thedeposition chamber is at about one atmosphere pressure, the carrier gasinitial pressure must be comparatively higher. The substrates would thenbe placed into the deposition chamber through the gas gate, and removedthrough another. In practice, these added complications and cost of thelost carrier gas, as well as the degree of control needed over thedeposition atmosphere, must be balanced against the need for continuousoperation.

An alternate embodiment, which may be preferred, in say, powderedmetallurgy applications is the mode of deposition described herein. Arotating drum 60, FIG. 4 is contained within the deposition chamber ofthe general apparatus previously described. The drum is substituted forthe general substrate. As the drum rotates, the portion of its surfacealigned into the jet changes, so the depositing 61 condensing at thestagnation point begin to coat the rotating drum's surface with a thinfilm. At another point on the drum's surface, is aligned a scraper 62which scrapes the thin film deposit off the rotating drum. The powderthus formed is collected in a hopper 64. Also described are mechanismsfor heating and cooling the rotating drum's surface in order tofacilitate the deposition and powdering processes. After the hopper isfilled with powder, the deposition is complete and the depositionchamber is opened to remove the product hopper of powder. This techniqueis highly useful for the controlled atmosphere evaporation andcondensation of materials needed for production of ultra pure powders ofthe so-called "super alloys", which are later compacted into verycritical parts such as helicopter rotor hubs, jet engine components,etc. Furthermore, the operation of my apparatus at the fairly highpressures that are allowable, would also facilitate merging theapparatus onto other high pressure devices for the controlled atmospherehandling and casting of powdered materials.

In an alternate embodiment, which would be the preferred embodiment forthe production of sheet or ribbon material by removing the product thinfilm deposit from the substrate, a rotating drum is placed in thedeposition chamber in place of the substrate. As shown in FIG. 12, ajet, carrying the depositing species 66, impinges on a drum 68, and thedepositing species 69 condenses in the stagnation point region. As thedrum rotates its surface through the stagnation point, a thin filmdeposit forms and coats the surface. At another point on the drum'ssurface, a knife 70 is positioned to peel the thin film deposit off thesurface. The product ribbon or sheet material 72 is pulled off thesurface with a mechanism 74. Elements for heating and cooling the drumsurface to facilitate the deposition and peeling processes areavailable. Such an apparatus, would be highly useful for the productionof thin metal foils, often used in electronics applications. Since thedrum can be maintained at high or low temperatures, high temperaturephases of metal alloys may be condensed and quenched into metastablephases at room temperature. In this manner the so called amorphousmetals may be produced. The device, in fact, appears similar in certainrespects to other rotating drum devices used to produce amorphous metalribbons, but these devices quench the metal from a melt, whereas mymethod involves quenching from the vapor phase.

Two rotating drum devices are used in preferred embodiments designedspecifically for the production of powdered materials and ribbonmaterials. These results could be obtained equally well with devicesemploying other "continuously" moving surfaces, say with a revolvingdisk, or a belt on spindles. Such simple alterations on the theme ofcontinuous motion of a surface are each not separately described.

DESCRIPTION OF FURTHER SPECIFIC EXAMPLES

Several experiments, which are specific examples of my invention wereperformed to demonstrate the concept of gas jet deposition. In theexperimental apparatus the carrier gas, and in certain instances diluteconcentrations of admixed reactant species, enters the apparatus.Subsequently it flows through a needle valve, which controls the massflux and then the flow is "choked" through a small orifice (0.2 mm indiameter). The pressure upstream is measured. A measurement of thepressure (P_(u)) upstream of the small orifice, is also an indirectmeasure of the mass flux, because the flow through the small orifice ismaintained supersonic, and then the mass flux is given by:

    m= 2/(γ+1)!.sup. γ/(γ-1)! (π d.sub.so Pu/4)< ρ/(R.sub.I T.sub.u)!                           (11)

where: γ.tbd.Specific heat ratio

d_(so) .tbd.Small orifice diameter

P_(u) .tbd.Pressure upstream (before expansion)

T_(u) .tbd.Temperature upstream

R_(I) .tbd.Ideal gas constant

In this case, the upstream temperature (T_(u)) could be assumed roomtemperature. For a given gas and orifice, the mass flux is thereforedependent only on the upstream pressure (P_(u)). In experiments, themass flux was approximately 5 milligrams per second.

After entering the nozzle, the gas flows over a tungsten filament (wire,0.2 mm in diameter, approx. 1 mm long) which is placed transverse to theflow, centered on the axis of the nozzle, and set within one nozzlediameter (d_(n) =2.0 mm) of the entrance to the nozzle throat section.This filament is heated resistively, and is the source of the depositingspecies. The gas entrains these species, expands through the nozzlethroat forming a jet that enters the deposition chamber with speed (U)and finally impacts on a glass plate, which is positioned several nozzlediameters downstream of the nozzle exit. The flow from the depositionchamber is removed by a mechanical pump at the rate of 160 liters perminute.

The pressure upstream of the nozzle could be measured at one position,whereas the base pressure in the deposition chamber was measured atanother position. A throttling valve permits regulation of the jet MachNumber, which is calculated assuming an isentropic expansion (a goodapproximation at high Reynolds Number), by the following Equation:

    M=√<< 2/(γ-1)! (P.sub.i /P.sub.b.sup. (1-γ)/γ! -1!>>                                                     (12)

where: P_(i) .tbd.Initial pressure upstream of nozzle

P_(b) .tbd.Base pressure in deposition chamber

All pressures were measured with either oil or mercury manometers, whilethe tungsten filament temperature (Tf) was measured using an opticalpyrometer.

The Reynolds Number of the jet can be calculated from the mass flux,given in Equation (11), since conservation of mass through the entiresystem (in steady state) requires:

    m=πρUd.sub.n.sup.2 /4                               (13)

where ρ.tbd.carrier gas density

d_(n) .tbd.Nozzle diameter

U.tbd.Jet velocity

The definition of the Reynolds Number (R) of the jet is:

    R.tbd.ρUd.sub.n /μ                                  (14)

where: μ.tbd.carrier gas viscosity

Upon substitution of (13) into (14),

    R=4m/(πμd.sub.n)                                     (15)

During operation the Reynold's Number was of order 100, which isactually not entirely large enough to satisfy the isentropic assumptionbehind the Mach Number calculation (Equation (12)). However, short of anumerical analysis, Equation 12 is the only means of estimating the MachNumber, and it should be fairly accurate at (R˜100).

These Equations for the Mach Number (M) (Equation 12) and the ReynoldsNumber (R) (eq. 14) are only valid for subsonic flow, and they neglectany energy addition by the hot filament. Also the specific heat ratio(γ) of the carrier gas only is used which neglects the presence of anyreactants in mixture. Still, these Equations should yield highlyaccurate estimates of the basic properties of the flow field--withintheir range of validity.

The experimental apparatus was used with one nozzle geometry to depositthree species for three separate demonstrations of the technique.

Experiment (1): A mixture of (0.5 molar %) silane in helium was flowedthrough the system. The upstream flow was maintained at pressure (P_(u)˜400 torr), while the filament was heated to temperature (T_(f) ˜2400°C.). At this temperature the silane decomposed at the filament intovarious condensing silicon-hydride radicals and a deposit formed on theglass slide. Deposition occurred over a fairly wide range of Mach Number(0.4<M<1). The initial pressure (P_(i))--pressure at thefilament--before expansion was of order 1 torr, while the base pressure(P_(b)) in the deposition chamber was correspondingly less, as thepressure ratio ranged over: (1.3<P_(i) /P_(B) <2).

Since the molecular mass ratio of silane to helium is only about eight(m_(d) /m_(c) ˜8), the dominant mechanism of deposition was surelydiffusion, at these subsonic flow velocities (M<1). The large pumpneeded to induce supersonic flow through this geometry was notavailable.

A nozzle with similar geometry, except that it had four times the throatlength was also tested. In this case, viscosity slowed the flowconsiderably and increased the residence time of the condensible speciesin the gas-phase. Significant nucleation of gas-phase clusters resultedand a particulate nature persisted in the morphology of the deposit.Indeed, a small change in apparatus geometry can have significantconsequence for the quality of the deposit.

An infra-red spectral analysis of the amorphous hydrogenated silicondeposit, formed by the first means showed no trace of atmosphericimpurities, thus demonstrating that the atmosphere during deposition wascontrolled.

Contaminant-free samples of hydrogenated amorphous-silicon in thin filmform can display semiconducting properties. Furthermore, these materialsmay be doped to form homojunctions. Dopants often used are boron andphosphorus. In my method, the doping of the hydrogenated amorphoussilicon can be achieved simply by premixing small concentrations(compared to the concentration of silane) of dopant bearing gases (e.gphosphene or diborene) into the flowing gas mixture of silane and theinert carrier gas. These dopant bearing species will dissociate at thehot surface of the filament just as the silane does, and the dopantsbearing radicals will then condense along with the silane and beincorporated in the amorphous-silicon solid. Such is one example ofusefulness of the reactant introduction mechanism, when it is beingemployed to introduce several differing reactant species.

Research has been reported in the literature, in which amorphous-siliconthin film materials alloyed with fluorine have been deposited in aplasma discharge apparatus from the gas-phase species,silicon-tetrafluoride. These materials display semiconducting propertiesas well. Silicon-tetrafluoride may be deposited in my apparatus, aswell, in a process exactly as above, except that (SiF₄) is substitutedfor (SiH₄).

Experiment (2): A small amount (˜1 molar %) of oxygen in helium wasflowed through the system from an upstream pressure (P_(u) ˜400 torr).The tungsten filament was maintained at a temperature (T_(f-) 1400° C.)at which surface oxidation occurs. The flow of oxygen oxidized thesurface of the tungsten, and the oxide evaporated from the filament, wasentrained in the helium flow, and formed a deposit. Experiments wereperformed over a wide range of Mach Number (0.1<M<1.0) and thereforeover a wide range of pressure ratios (1<P_(i) /P_(b) <2) to study theeffect of inertia on the deposition. The pressures throughout the nozzlesystem were always of order 1 torr. At low velocity, the deposits werebroad, implying that the tungstic-oxide molecules had time to diffuseradially in the jet. At high velocity, however, the opposite was true;the molecules were inertially impacted and concentrated near thestagnation point.

Thus is demonstrated a fairly general method of depositing metal-oxidethin film coating. Of course, such insulating thin film layers made frommetal-oxides (e.g. aluminum-oxide, or magnesium-oxide) are highly usefulas parts of electronic devices. Certain oxides can have usefulconducting properties as well (e.g. ITO, MbSnO₄ or SnO₂ (Sb doped)).

Silicon-oxide thin films are also used as constituents in electronicdevices. This species can be co-deposited with glass forming dopants orcrystal forming dopant (depending on the final application). The methodwould be to premix silane gas into the stream of inert carrier gasupstream of the nozzle (introductory method 1. Dopant bearing species(e.g. diborene) could also be premixed in the inert carrier-silanemixture in the concentration chosen so that the thin film deposit hasthe desired dopant concentration. In flow region 34, oxygen can beintroduced via a separate thin tube (delivery mechanism 3). The silaneand dopant bearing species will oxidize and the resulting silicon-oxideand small concentrations of dopant-oxide (along with residual hydrogenatoms) will condense to form a deposit at the stagnation point on thesubstrate. Subsequent annealing can be employed to drive off anyunwanted hydrogen. An alternate mechanism involves the evaporation ofsilicon atoms from solid silicon (delivery mechanism 2) into the inertcarrier into which oxygen molecules have previously been seeded(delivery mechanism 1). The process of silicon-oxide deposition issimilar to the aluminum-oxide deposition. The process will be useful inthe coating of glass optical fibers, and can have other applications inthe deposition of useful glass thin films.

It is recognized that metal-oxides coating are also useful for theireffectiveness in providing chemical protection for the supportingsubstrate material at elevated temperatures. Powdered metal-oxide alsocan be useful in ceramics.

In alternate applications, other species (e.g. nitrogen, chlorine) maybe substituted as the gas-phase oxidizing species premixed in the flowof the inert carrier, which oxidizes the heated metal. For example,titanium may be the evaporated metal atoms which oxidize with nitrogenmolecules admixed in the inert gas flow. In this manner titanium-nitridecoatings could be formed on substrate surfaces. Titanium-nitride thinfilms are valued for their extreme hardness, and so if the substratewere, say, a cutting tool, then the titanium-nitride deposit would serveas a tool coating material.

In other specific applications involving the production of metal-oxidedeposits, rather than evaporating the metal atoms from a pure solidmetal sample (the reactant species introduction mechanism 2), the metalatoms would first be introduced as part of a chemical species (e.g ametal-carbonyl) which has a fairly high vapor pressure at normal (i.e.around room) temperatures. Thus, such a species could easily be premixedin the inert carrier fluid (introduction mechanism 1) while theoxidizing species would be introduced via a thin tube into the reactionregion 34 of the flow field (delivery mechanism 3). In this manner, theoxidation reaction would occur in the flow region R1 thus producing acondensible metal-oxide radical to be deposited on the preparedsubstrate in the usual manner.

Experiment (3): Starting from upstream pressure (P_(u) ˜400 torr), purehelium was flowed through the system, and over a gold foil that waswrapped around the tungsten filament. The filament was heated totemperatures at which gold atoms evaporated; these were transported bythe jet, and deposited. Again deposition could be induced to proceedover a wide range of Mach Number (0.1<M<1). Again the initial and basepressures were of order 1 torr. Thus is demonstrated a general methodfor the deposition of thin solid metal films. Since the metal atoms areintroduced into the gas-phase by delivery mechanism 2, the metalmaterial in the flow region 34 is heated to elevated temperatures, yetthe substrate in region 38 can remain cool. This would allow thefabrication of solid metal thin film coatings on materials (e.g.plastic, paper, etc.) which cannot sustain high temperatures. Such ametal film could have application as a conducting layer in an electronicdevice. Also, catalyst materials (e.g platinum) can be deposited in thinfilm form in a like manner.

The evaporative coating of metals could be employed in conjunction withapparatus described to produce metal foils. The high quench ratesaffordable by my method makes possible the condensation and productionof amorphous metal ribbons, which materials can have unusually highstrength due to their lack of the line defects of a crystal lattice.

Several metals can be evaporated simultaneously, from several pure metalsolid metal samples, each placed and heated in the region 34 of the flowfield (multiple use of delivery mechanism 2). In this manner metalalloys may be produced. For example, titanium-nickel, or aluminum nickelalloy thin film deposits (usually produced by cosputtering) can beproduced. These thin film materials, when alloyed properly with a smallconcentration of a ternary element (usually a rare-earth metal), candisplay large capacity for the chemisorption of hydrogen. Using such amaterial as a hydrogen storage system can have application in batteryand fuel cell technology.

Chromium-cobalt compounds in thin film coating form have recently foundapplication in electronic information storage technology, as a materialused in computer disk memory devices.

Organic molecules as well may be deposited to form coatings. Organicmaterials in bulk solid form (e.g. anthracene) may be heated toevaporate the long chain molecules into the gas-phase, so they may beconvected by the inert carrier gas flow. The substrate may be heated orcooled during deposition to encourage or suppress further polymerizationand crosslinking of the long chain molecules that have condensed ontothe substrates surface. Alternately, monomers may be synthesized in thegas phase and then allowed to polymerize during their transport in thejet to the substrate, where they condense. The constituent reactants ofsuch gas-phase synthesis reactions may be introduced into the flow viathe mechanisms previously described. Polymeric coatings can have usefulinsulating properties; they are used as chemical protective coatings,and certain polymers are known to have conducting and semiconductingproperties.

These three demonstrations indicate the general method which is employedto make many various thin solid film materials. These films may beeither conducting, semiconducting or insulating, but their uses are notlimited to exploiting their electronic properties.

As will be seen, I have disclosed a method and apparatus with which canbe deposited conductors and dielectrics as products such as solid layersor thin film (and then, if desired, further processed to power) composedof the following chemical species: Silicon, gold, tungsten, aluminum,magnesium, iron, carbon, chromium, cobalt, platinum, titanium, germaniumand other metals; solid phases of oxides, nitrides, hydrides, fluorides,and other compounds containing an oxidizing agent; including mixturesand alloys and compounds thereof in either crystal, polycrystal oramorphous phase. In addition the product can be an organic solid or apolymer. Additional understanding of the inventions disclosed will befound upon a reading of the claims of this disclosure.

We claim:
 1. An apparatus for depositing a condensable gaseous materialentrained in an inert carrier gas as a solid film on a substrate, saidapparatus comprising:(a.) a deposition chamber having a plurality ofports; (b.) carrier gas means for supplying an inlet flow of carrier gasto a first port; (c.) a gas jet nozzle means positioned on a one of saiddeposition chamber ports having an interior cavity bounded by aninterior cavity wall, an inlet port and an outlet orifice positioned ata distal end of said nozzle cavity from said gas jet inlet port, saidgas jet means positioned within said chamber for receiving said carriergas at said inlet port and generating a high speed gas jet through saidgas jet nozzle means interior cavity with a selected gas jet speed Machnumber at the orifice of at least 0.1 and for presenting said high speedgas jet to said chamber through said orifice; (d.) a means for locatingthe substrate within said deposition chamber: at a first substrateposition to receive said high speed gas jet at a substrate uppersurface; (e.) a means for generating condensable gaseous material forpresentation to the high speed gas jet so as to entrain said gaseouscondensable material within said carrier gas jet away from said interiorcavity wall; (f.) a transport means for effecting relative lateralmovement between said gas jet and the substrate so as to deposit saidentrained condensable gaseous material on said substrate upper surfaceforming a film with a uniform thickness; and (g.) a pump means forevacuating gas from said deposition chamber at a How rate that maintainssaid carrier gas jet speed at the selected Mach number and at a pressurebelow atmospheric pressure.
 2. Apparatus according to claim 1, furthercomprising means for heating and cooling said substrate.
 3. Apparatusaccording to claim 1, further comprising means for heating and coolingsaid inert carrier gas.
 4. Apparatus according to claim 1, furthercomprising means for recirculating inert carrier gas from said gasoutlet to said gas inlet.
 5. Apparatus according to claim 1, whereinsaid jet forming means includes a nozzle for controlling thethermodynamic and gas-dynamic flow conditions in order to promote andoptimize chemical synthesis reactions taking place in said gas stream.6. Apparatus according to claim 1, wherein said substrate is in the formof a body having an overall breadth much greater than the width of saidjet.
 7. Apparatus as claimed in claim 1, wherein said substrate has asharp edge.
 8. Apparatus as claimed in claim 1, wherein said substratehas a breadth and curvature coextensive with the width and curvature ofsaid jet.
 9. Apparatus as claimed in claim 1, wherein means are providedfor removing deposited material from a stagnation point on the surfaceof said substrate at which point said jet impinges, whereby the removedmaterial is powdered.
 10. Apparatus according to claim 1, wherein meansare provided for removing deposited material from said substrate surfacein ribbon or sheet form.
 11. The apparatus of claim 1 wherein saidcondensable gaseous material generation means further comprises a meansfor generating said condensable gaseous material contiguous to said gasjet nozzle means.
 12. The apparatus of claim 1 wherein said condensablegaseous material generation means further comprises a means forgenerating said condensable material within said gas jet nozzle means.13. The apparatus of claim 1 wherein said condensable gaseous materialgeneration means further comprises a means for generating condensablegaseous material downstream of said orifice.
 14. The apparatus of claim1 wherein said condensable gaseous material generation means furthercomprises an electron beam means for generating said condensablematerial.
 15. The apparatus of claim 1 further comprising a second gasjet nozzle means mounted on a second deposition chamber port to presenta second gas jet to said substrate at a second substrate position, saidapparatus further comprising; a translation means to provide movement ofsaid substrate relative to said gas jet nozzle means between said firstand second substrate positions.
 16. The apparatus of claim 1 whereinsaid condensable gaseous material generation means further comprises ameans for generating said condensable gaseous material so as to formclusters of said condensable material atoms at said substrate uppersurface.
 17. The apparatus of claim 1 wherein said condensable said gasgeneration means further comprises a means for generating molecules of aprecursor species destined for consumption in an evolving synthesisreaction occurring in the flow medium are mixed with a carrier gas as anundersaturated vapor before depositing species synthesis.
 18. Theapparatus of claim 1 wherein said condensable gas deposition apparatusfurther comprises a means for generating chemical species destined forconsumption in an evolving chemical synthesis reactions in fluid formdelivered by means of a thin tube exiting into the gas jet.
 19. Theapparatus of claim 1 wherein said condensable material generation meansfurther comprises a means for generating one of the following chemicalspecies: silicon, gold, copper, tungsten, aluminum, magnesium, iron,carbon, chromium, cobalt, platinum, titanium and germanium; solid phasesof oxides, nitrides, hydrides, fluorides and other compounds containingan oxidizing agent or combination thereof, including mixtures and alloysand compounds thereof in either crystal, polycrystal or amorphous phase.20. The apparatus of claim 1 wherein said gas jet means furthercomprises a means for controlling the flow of said gas jet to have aspeed in excess of 0.4 Mach number.
 21. The apparatus of claim 20wherein said gas jet means further comprises a means for providing saidgas jet in excess of Mach
 1. 22. The apparatus of claim 1 furthercomprising a means for providing a continuous flow of inert gas throughthe deposition chamber, thereby continuously purging the depositionchamber.
 23. The apparatus of claim 1 wherein said pumping means furthercomprises a means for maintaining gas pressure in the deposition chamberbetween 0.1 and 50 Torr.
 24. The apparatus of claim 1 wherein said meansfor generating condensable gaseous material further comprises a meansfor simultaneous presentation of a plurality of condensable gaseousmaterials.
 25. The apparatus of claim 1 wherein said means forgenerating condensable gaseous material further comprising a means ameans for generating plasma discharge.
 26. The apparatus of claim 1wherein said means for generating condensable gaseous material furthercomprising a means for presenting a combination of first and secondcondensable gaseous materials to said high speed gas jet, therebydepositing a compound or alloy film.
 27. The apparatus of claim 1wherein said means for generating condensable gaseous material furthercomprising a means for sequentially presenting a combination of firstand second condensable gaseous materials to said high speed gas jet;thereby depositing a multilayer film.
 28. The apparatus of claim 1further comprising a means for presenting a continuous substrate to saidgas jet.